This field of crescent-shaped dunes (lat.73.62, lon. 328.215) is located just south of the North Polar layered terrain.
These dunes, known as barchan dunes, usually form where there is a moderate supply of sand and a prevailing wind direction. The “arms” or “horns” of barchan dunes point in the downwind direction and in this case indicate that the prevailing winds blow towards the northwest.
The dunes in the close-up image are approximately 100 meters across and are traversing a bumpy, hard terrain. Polygonal patterns are evident in some areas while numerous meter-scale boulders are strewn throughout the region. The boulders are more numerous in areas where the polygonal patterns are less pronounced. Repeat imaging of this dune field could reveal whether these dunes are presently moving.
Written by: Ginny Gulick (audio by Tre Gibbs) (11 July 2012)
More info and image formats at http://hirise.lpl.arizona.edu/ESP_027378_2540
Image: NASA/JPL/University of Arizona